1. Field of the Invention
This invention relates to a drive control device in a vibration wave motor utilizing ultrasonic vibration.
2. Related Background Art
Ultrasonic vibration motors are already known, for example, from U.S. Pat. Nos. 4,510,411 and 4,562,374.
Vibration motors of this type are such that for example, an AC signal is supplied to an electrostrictive device to vibrate it, thereby forming a travelling vibration wave in the surface of a resilient member and driving a moving member. At this time, the moving member is in contact with the resilient member with a predetermined pressure force and thus, when the load of the moving member becomes great, relative displacement based on the travelling vibration wave occurs between the surfaces of contact of the two members Accordingly, to prevent the abrasion of the two members and improve their lives, it is preferable to stop the motor when the load of the moving member is great. There is also a requirement that when the moving member is locked, it should be detected to reverse the motor.
So, it is conceivable to provide a sensor such as a rotary encoder on the moving member side and detect from the movement of the moving member that a great load is acting, to thereby stop the vibration wave motor, or to provide a switch adapted to be closed in a predetermined rotation angle position of the moving member and stop or reverse the motor by the closing of this switch, but this is not preferable in that a sensor or a switch discrete from the motor components is necessary, which in turn leads to a complicated construction. It is not possible to detect an overcurrent and detect the motor load as in the conventional DC motors.